UPDATE: Seth Finkelstein has done some great research on this. He finds that many sites were blocked because they used to have objectionable content, shows how it's implemented using a post-processing step, demonstrates improved search techniques and strategies, and notes that it also affects Google Images and Directory.
Jonathan Zittrain and Benjamin Edelman have released their latest report, systematic documentation of how Google.de and Google.fr filter controvertial sites. Google gives no notice that results are being filtered (as they do with the DMCA) and have nothing about it on their website (although they did acknowledge the practice in one email I found). Declan McCullagh asked for a list of blocked sites but Google refused to supply one.
The authors list 113 sites they found thru trial-and-error to be blocked and again let you submit your own and record the results.
Disclaimer: I assisted the authors with portions of the report.
Posted by Aaron Swartz on October 24, 2002 08:53 PM